Bisphenol A, or BPA, is a chemical found in plastics, including food packaging, that may interfere with the way our cells work. Are we exposed to enough BPA to harm us? And should we be afraid of the alternative products with their “BPA free” stickers? Let’s just say...it’s complicated.

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What Is BPA?

Remember when Nalgene bottles were the hot new thing? In the early 2000s we didn’t have jet packs, but we did have hard plastic water bottles that were made of the same stuff that’s in bulletproof glass. They didn’t break when you dropped them, and they didn’t leach a plastic-y taste into your water. It was the future. The future was good.

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These bottles were made of a tough plastic called polycarbonate, or more specifically polycarbonate of bisphenol A. Here’s what bisphenol A, or BPA, looks like:

If you want to make polycarbonate plastic, you’ll need some BPA, another molecule called phosgene (this provides the “carbonate” portion), and a few other chemicals to join them together into a chain that goes BPA-carbonate-BPA-carbonate-BPA-carbonate. All plastics, or polymers, are chains like this: polyethylene is a chain of ethylenes, polystyrene is a chain of styrenes, and so on. Here’s what polycarbonate of BPA plastic looks like (the brackets indicate repetition):

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Nothing lasts forever, not even super-strong plastics. Over time, polymers break down, and their pieces can break off from the chain. The BPA in the chains can’t hurt you, but people are worried about the BPA building blocks that work their way free. Heat speeds up the breakdown process, so anything that gets microwaved or left out in the sun is more likely to contain the BPA people worry about.

Is BPA Harmful?

If someone handed you a glass of estrogen, you wouldn’t chug it. But a drink of water from a polycarbonate bottle is nowhere near the same thing. First, there’s very little BPA leaching out of the bottle into your water; and second, BPA binds more weakly than estrogen by a factor of 10,000.

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The question isn’t whether BPA can act like estrogen—we know it can. The question is whether the amount that leaches out of your water bottle (and the liners of canned foods, and the thermal paper store receipts are printed on) is anywhere near enough to be harmful. Some scientists and environmental groups say it is; others, including those with ties to the plastics industry, say it isn’t.

Here’s a little survey of who’s saying what:

The World Health Organization concluded in 2010 that the evidence varies from “no health concerns” in some cases to insufficient data in others.

The US Food and Drug Administration wrote in 2014 that “an adequate margin of safety exists for BPA at current levels of exposure from food contact uses” (in other words, can liners and other packaging) and that “BPA is safe at the current levels occurring in foods.”

The European Food Safety Authority concluded in January 2015 that there is “nohealth concern for any age group from dietary exposure and low health concern from aggregated exposure.”

The Endocrine Society wrote in a 2015 review that recent research “removes any doubt that [endocrine disruptors like BPA] are contributing to increased chronic disease burdens related to obesity, diabetes mellitus, reproduction, thyroid, cancers, and neuroendocrine and neurodevelopmental functions.”

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Those conclusions hide mountains of controversy. There’s no strong, definitive evidence showing BPA to be harmful—but it’s hard to know what to believe when the better studies are industry-funded, and the “independent” studies are small and can’t be reproduced.

That’s just one of the criticisms in a 2005 paper in Environmental Health Perspectives that puts forth the case that BPA is toxic at low doses, and decades of research have been completely missing that fact. Most substances follow a straightforward dose-response relationship: the more alcohol you drink, for example, the drunker you get. To argue that BPA is dangerous at low levels, researchers have to argue that BPA doesn’t follow that rule. Statistician Patrick McKnight reviewed that idea for Sense About Statistics, and found the research on low-dose effects to be a mess. It’s possible that low doses are dangerous, but the current evidence doesn’t make a convincing case. We still need to do more research.

That’s the conclusion of almost every study, whether pro or con: there’s not enough research on BPA. Or more accurately, there’s been a lot of research, but it doesn’t usually answer the questions we’re most curious about. For example, there’s been very little research on the effects of BPA in actual living human beings. Most of the work has been in laboratory dishes of cells, or the effects on rats and fish.

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And yet, for as little as we know about BPA, we know even less about the chemicals in “BPA free” plastics. One of BPA’s replacements is bisphenol S, which also seems to be an endocrine disruptor. A study of over 500 plastic products, published in Environmental Health Perspectives and conducted by a testing lab that has made enemies in the plastics industry, found that “almost all” of the plastic products it tested showed estrogenic activity, including ones labeled “BPA free.”

If You Want to Avoid BPA

I hate to be alarmist. You probably don’t need to avoid BPA. There’s a good chance it will turn out that low doses aren’t a problem, but we don’t have enough evidence to be totally sure. There’s no harm in swapping plastics for other materials, especially if you find you prefer their looks or functionality.

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If you’re avoiding BPA-containing plastics as a precaution, you should probably avoid other plastics too. After all, new chemicals don’t have to be proven safe before they hit the market. So if a label on a bottle says “BPA free,” that means it’s missing a chemical that has been studied, and instead has a newer chemical that we know nothing about. Maybe it’s better, maybe worse. If you want to avoid plastics with possible endocrine disruptors, here are some strategies that might help:

Choose non-plastics, like glass and stainless steel. These options are available, though usually more expensive, for things like food containers and water bottles. Milk that mason jar trend while you still can!

Avoid microwaving plastic containers, or otherwise exposing them to stresses like heat and sunlight. Even if you use plastic to store food, you could transfer the food to a bowl to microwave, and make sure to hand-wash the plastic container instead of putting it in the dishwasher.

Avoid canned foods, since cans are lined with an epoxy that typically contains BPA. Fresh or frozen food doesn’t have the same concern. Tetra packs, those square juice box-like containers, use a plastic that hasn’t (yet) been connected to estrogenic activity.

Don’t lick your receipts. Yeah, you laugh, but you’re not a six-month-old baby. At that age, my kids thought receipts were delicious. Casually handling a receipt with your dry hands doesn’t raise the BPA levels in your body, even though they do contain the chemical, so if that’s all you do with them, you’re probably fine.

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Some people go to great lengths to avoid having plastics in their life. If that feels like overkill, consider using these tips some of the time. For example, I store leftovers in glass containers at home, even though I still use plastic when I pack a lunch to go. Maybe these precautions will seem silly in 50 years, but for now this feels about right.